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 $232.53   9.158%   $253.8251   $253.83   $253.85   $253.80  
  Purchase #2 $204.87   10.766%   $226.9263   $226.93   $226.95   $226.90  
  Purchase #3 $196.97   11.716%   $220.047   $220.05   $220.05   $220.00  
  Purchase #4 $184.47   11.481%   $205.649   $205.65   $205.65   $205.60  
  Purchase #5 $102.88   7.456%   $110.5507   $110.55   $110.55   $110.60  
  Purchase #6 $100.47   7.681%   $108.1871   $108.19   $108.20   $108.20  
  Purchase #7 $62.71   4.779%   $65.7069   $65.71   $65.70   $65.70  
  7 purchase totals = $1,084.90       $1,190.8921   $1,190.91   $1,190.95   $1,190.80