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 $68.32   7.802%   $73.6503   $73.65   $73.65   $73.70  
  Purchase #2 $248.91   7.333%   $267.1626   $267.16   $267.15   $267.20  
  Purchase #3 $132.32   12.834%   $149.3019   $149.30   $149.30   $149.30  
  Purchase #4 $25.76   5.346%   $27.1371   $27.14   $27.15   $27.10  
  Purchase #5 $160.57   12.214%   $180.182   $180.18   $180.20   $180.20  
  Purchase #6 $246.31   5.360%   $259.5122   $259.51   $259.50   $259.50  
  Purchase #7 $60.60   5.836%   $64.1366   $64.14   $64.15   $64.10  
  7 purchase totals = $942.79       $1,021.0827   $1,021.08   $1,021.10   $1,021.10