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 $51.26   5.499%   $54.0788   $54.08   $54.10   $54.10  
  Purchase #2 $97.43   13.533%   $110.6152   $110.62   $110.60   $110.60  
  Purchase #3 $14.49   9.196%   $15.8225   $15.82   $15.80   $15.80  
  Purchase #4 $212.61   3.453%   $219.9514   $219.95   $219.95   $220.00  
  Purchase #5 $232.35   7.861%   $250.615   $250.62   $250.60   $250.60  
  Purchase #6 $203.42   3.284%   $210.1003   $210.10   $210.10   $210.10  
  Purchase #7 $204.72   5.529%   $216.039   $216.04   $216.05   $216.00  
  7 purchase totals = $1,016.28       $1,077.2222   $1,077.23   $1,077.20   $1,077.20