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 $67.70   11.616%   $75.564   $75.56   $75.55   $75.60  
  Purchase #2 $209.98   13.145%   $237.5819   $237.58   $237.60   $237.60  
  Purchase #3 $191.38   9.626%   $209.8022   $209.80   $209.80   $209.80  
  Purchase #4 $150.67   8.362%   $163.269   $163.27   $163.25   $163.30  
  Purchase #5 $176.47   11.557%   $196.8646   $196.86   $196.85   $196.90  
  Purchase #6 $65.65   4.551%   $68.6377   $68.64   $68.65   $68.60  
  Purchase #7 $62.86   10.301%   $69.3352   $69.34   $69.35   $69.30  
  7 purchase totals = $924.71       $1,021.0546   $1,021.05   $1,021.05   $1,021.10