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 $80.73   11.397%   $89.9308   $89.93   $89.95   $89.90  
  Purchase #2 $106.96   9.736%   $117.3736   $117.37   $117.35   $117.40  
  Purchase #3 $69.64   7.813%   $75.081   $75.08   $75.10   $75.10  
  Purchase #4 $187.47   8.104%   $202.6626   $202.66   $202.65   $202.70  
  Purchase #5 $240.25   10.850%   $266.3171   $266.32   $266.30   $266.30  
  Purchase #6 $173.80   9.778%   $190.7942   $190.79   $190.80   $190.80  
  Purchase #7 $216.53   10.768%   $239.846   $239.85   $239.85   $239.80  
  7 purchase totals = $1,075.38       $1,182.0053   $1,182.00   $1,182.00   $1,182.00