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 $61.91   10.753%   $68.5672   $68.57   $68.55   $68.60  
  Purchase #2 $98.64   8.513%   $107.0372   $107.04   $107.05   $107.00  
  Purchase #3 $62.29   7.305%   $66.8403   $66.84   $66.85   $66.80  
  Purchase #4 $142.60   5.164%   $149.9639   $149.96   $149.95   $150.00  
  Purchase #5 $77.32   10.688%   $85.584   $85.58   $85.60   $85.60  
  Purchase #6 $201.56   4.660%   $210.9527   $210.95   $210.95   $211.00  
  Purchase #7 $16.40   6.802%   $17.5155   $17.52   $17.50   $17.50  
  7 purchase totals = $660.72       $706.4608   $706.46   $706.45   $706.50