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 $60.34   12.278%   $67.7485   $67.75   $67.75   $67.70  
  Purchase #2 $134.80   6.571%   $143.6577   $143.66   $143.65   $143.70  
  Purchase #3 $99.30   6.832%   $106.0842   $106.08   $106.10   $106.10  
  Purchase #4 $91.79   13.562%   $104.2386   $104.24   $104.25   $104.20  
  Purchase #5 $122.61   12.830%   $138.3409   $138.34   $138.35   $138.30  
  Purchase #6 $223.66   5.818%   $236.6725   $236.67   $236.65   $236.70  
  Purchase #7 $172.55   13.361%   $195.6044   $195.60   $195.60   $195.60  
  7 purchase totals = $905.05       $992.3468   $992.34   $992.35   $992.30