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 $207.73   11.663%   $231.9575   $231.96   $231.95   $232.00  
  Purchase #2 $200.36   5.771%   $211.9228   $211.92   $211.90   $211.90  
  Purchase #3 $166.53   6.863%   $177.959   $177.96   $177.95   $178.00  
  Purchase #4 $92.47   7.341%   $99.2582   $99.26   $99.25   $99.30  
  Purchase #5 $24.58   11.450%   $27.3944   $27.39   $27.40   $27.40  
  Purchase #6 $176.57   7.391%   $189.6203   $189.62   $189.60   $189.60  
  Purchase #7 $82.52   12.741%   $93.0339   $93.03   $93.05   $93.00  
  7 purchase totals = $950.76       $1,031.1461   $1,031.14   $1,031.10   $1,031.20