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 $6.53   10.474%   $7.214   $7.21   $7.20   $7.20  
  Purchase #2 $180.29   11.700%   $201.3839   $201.38   $201.40   $201.40  
  Purchase #3 $181.75   8.493%   $197.186   $197.19   $197.20   $197.20  
  Purchase #4 $48.53   10.632%   $53.6897   $53.69   $53.70   $53.70  
  Purchase #5 $229.28   5.184%   $241.1659   $241.17   $241.15   $241.20  
  Purchase #6 $39.25   13.300%   $44.4703   $44.47   $44.45   $44.50  
  Purchase #7 $203.42   12.531%   $228.9106   $228.91   $228.90   $228.90  
  7 purchase totals = $889.05       $974.0204   $974.02   $974.00   $974.10