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 $49.63   4.324%   $51.776   $51.78   $51.80   $51.80  
  Purchase #2 $228.35   9.402%   $249.8195   $249.82   $249.80   $249.80  
  Purchase #3 $57.65   10.582%   $63.7505   $63.75   $63.75   $63.80  
  Purchase #4 $61.42   4.368%   $64.1028   $64.10   $64.10   $64.10  
  Purchase #5 $214.72   13.625%   $243.9756   $243.98   $244.00   $244.00  
  Purchase #6 $231.90   9.276%   $253.411   $253.41   $253.40   $253.40  
  Purchase #7 $226.49   6.273%   $240.6977   $240.70   $240.70   $240.70  
  7 purchase totals = $1,070.16       $1,167.5331   $1,167.54   $1,167.55   $1,167.60