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 $149.48   8.751%   $162.561   $162.56   $162.55   $162.60  
  Purchase #2 $99.91   7.557%   $107.4602   $107.46   $107.45   $107.50  
  Purchase #3 $62.35   10.630%   $68.9778   $68.98   $69.00   $69.00  
  Purchase #4 $190.57   11.742%   $212.9467   $212.95   $212.95   $212.90  
  Purchase #5 $174.73   7.817%   $188.3886   $188.39   $188.40   $188.40  
  Purchase #6 $76.32   10.168%   $84.0802   $84.08   $84.10   $84.10  
  Purchase #7 $169.53   5.564%   $178.9626   $178.96   $178.95   $179.00  
  7 purchase totals = $922.89       $1,003.3771   $1,003.38   $1,003.40   $1,003.50