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 $160.49   8.548%   $174.2087   $174.21   $174.20   $174.20  
  Purchase #2 $129.74   6.434%   $138.0875   $138.09   $138.10   $138.10  
  Purchase #3 $23.53   5.386%   $24.7973   $24.80   $24.80   $24.80  
  Purchase #4 $110.75   13.792%   $126.0246   $126.02   $126.00   $126.00  
  Purchase #5 $178.49   8.142%   $193.0227   $193.02   $193.00   $193.00  
  Purchase #6 $125.94   9.822%   $138.3098   $138.31   $138.30   $138.30  
  Purchase #7 $228.29   5.793%   $241.5148   $241.51   $241.50   $241.50  
  7 purchase totals = $957.23       $1,035.9654   $1,035.96   $1,035.90   $1,035.90