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 $78.69   12.104%   $88.2146   $88.21   $88.20   $88.20  
  Purchase #2 $183.94   11.194%   $204.5302   $204.53   $204.55   $204.50  
  Purchase #3 $179.37   13.546%   $203.6675   $203.67   $203.65   $203.70  
  Purchase #4 $63.56   3.702%   $65.913   $65.91   $65.90   $65.90  
  Purchase #5 $92.97   3.485%   $96.21   $96.21   $96.20   $96.20  
  Purchase #6 $220.68   7.770%   $237.8268   $237.83   $237.85   $237.80  
  Purchase #7 $125.73   9.782%   $138.0289   $138.03   $138.05   $138.00  
  7 purchase totals = $944.94       $1,034.3910   $1,034.39   $1,034.40   $1,034.30