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 $108.38   11.747%   $121.1114   $121.11   $121.10   $121.10  
  Purchase #2 $177.72   7.816%   $191.6106   $191.61   $191.60   $191.60  
  Purchase #3 $121.98   13.634%   $138.6108   $138.61   $138.60   $138.60  
  Purchase #4 $119.32   11.159%   $132.6349   $132.63   $132.65   $132.60  
  Purchase #5 $73.96   5.481%   $78.0137   $78.01   $78.00   $78.00  
  Purchase #6 $235.63   13.620%   $267.7228   $267.72   $267.70   $267.70  
  Purchase #7 $244.84   7.787%   $263.9057   $263.91   $263.90   $263.90  
  7 purchase totals = $1,081.83       $1,193.6099   $1,193.60   $1,193.55   $1,193.50