Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $237.90   10.822%   $263.6455   $263.65   $263.65   $263.60  
  Purchase #2 $111.41   9.824%   $122.3549   $122.35   $122.35   $122.40  
  Purchase #3 $184.85   10.842%   $204.8914   $204.89   $204.90   $204.90  
  Purchase #4 $116.62   12.754%   $131.4937   $131.49   $131.50   $131.50  
  Purchase #5 $31.35   7.814%   $33.7997   $33.80   $33.80   $33.80  
  Purchase #6 $127.49   7.341%   $136.849   $136.85   $136.85   $136.80  
  Purchase #7 $231.72   7.468%   $249.0248   $249.02   $249.00   $249.00  
  7 purchase totals = $1,041.34       $1,142.0590   $1,142.05   $1,142.05   $1,142.00