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 $138.79   10.205%   $152.9535   $152.95   $152.95   $153.00  
  Purchase #2 $22.60   7.501%   $24.2952   $24.30   $24.30   $24.30  
  Purchase #3 $185.92   8.412%   $201.5596   $201.56   $201.55   $201.60  
  Purchase #4 $125.45   12.257%   $140.8264   $140.83   $140.85   $140.80  
  Purchase #5 $219.78   5.802%   $232.5316   $232.53   $232.55   $232.50  
  Purchase #6 $48.68   6.206%   $51.7011   $51.70   $51.70   $51.70  
  Purchase #7 $203.86   13.299%   $230.9713   $230.97   $230.95   $231.00  
  7 purchase totals = $945.08       $1,034.8387   $1,034.84   $1,034.85   $1,034.90