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 $189.28   6.713%   $201.9864   $201.99   $202.00   $202.00  
  Purchase #2 $230.51   11.781%   $257.6664   $257.67   $257.65   $257.70  
  Purchase #3 $151.35   11.719%   $169.0867   $169.09   $169.10   $169.10  
  Purchase #4 $217.65   13.402%   $246.8195   $246.82   $246.80   $246.80  
  Purchase #5 $31.40   6.869%   $33.5569   $33.56   $33.55   $33.60  
  Purchase #6 $248.56   10.474%   $274.5942   $274.59   $274.60   $274.60  
  Purchase #7 $80.96   3.733%   $83.9822   $83.98   $84.00   $84.00  
  7 purchase totals = $1,149.71       $1,267.6923   $1,267.70   $1,267.70   $1,267.80