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 $193.53   11.185%   $215.1763   $215.18   $215.20   $215.20  
  Purchase #2 $5.52   7.590%   $5.939   $5.94   $5.95   $5.90  
  Purchase #3 $207.93   11.585%   $232.0187   $232.02   $232.00   $232.00  
  Purchase #4 $177.45   10.770%   $196.5614   $196.56   $196.55   $196.60  
  Purchase #5 $83.39   4.619%   $87.2418   $87.24   $87.25   $87.20  
  Purchase #6 $67.40   9.368%   $73.714   $73.71   $73.70   $73.70  
  Purchase #7 $132.89   5.562%   $140.2813   $140.28   $140.30   $140.30  
  7 purchase totals = $868.11       $950.9325   $950.93   $950.95   $950.90