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 $43.38   12.848%   $48.9535   $48.95   $48.95   $49.00  
  Purchase #2 $204.61   11.559%   $228.2609   $228.26   $228.25   $228.30  
  Purchase #3 $31.66   8.157%   $34.2425   $34.24   $34.25   $34.20  
  Purchase #4 $241.91   13.766%   $275.2113   $275.21   $275.20   $275.20  
  Purchase #5 $141.37   5.721%   $149.4578   $149.46   $149.45   $149.50  
  Purchase #6 $53.31   12.733%   $60.098   $60.10   $60.10   $60.10  
  Purchase #7 $194.43   11.514%   $216.8167   $216.82   $216.80   $216.80  
  7 purchase totals = $910.67       $1,013.0407   $1,013.04   $1,013.00   $1,013.10