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 $50.29   9.282%   $54.9579   $54.96   $54.95   $55.00  
  Purchase #2 $138.44   3.180%   $142.8424   $142.84   $142.85   $142.80  
  Purchase #3 $193.65   8.637%   $210.3756   $210.38   $210.40   $210.40  
  Purchase #4 $195.55   3.249%   $201.9034   $201.90   $201.90   $201.90  
  Purchase #5 $65.98   3.301%   $68.158   $68.16   $68.15   $68.20  
  Purchase #6 $157.95   5.790%   $167.0953   $167.10   $167.10   $167.10  
  Purchase #7 $74.52   6.475%   $79.3452   $79.35   $79.35   $79.30  
  7 purchase totals = $876.38       $924.6778   $924.69   $924.70   $924.70