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 $82.47   12.764%   $92.9965   $93.00   $93.00   $93.00  
  Purchase #2 $128.89   10.114%   $141.9259   $141.93   $141.95   $141.90  
  Purchase #3 $11.83   3.151%   $12.2028   $12.20   $12.20   $12.20  
  Purchase #4 $93.82   3.220%   $96.841   $96.84   $96.85   $96.80  
  Purchase #5 $138.96   11.361%   $154.7472   $154.75   $154.75   $154.70  
  Purchase #6 $232.74   9.313%   $254.4151   $254.42   $254.40   $254.40  
  Purchase #7 $231.47   8.619%   $251.4204   $251.42   $251.40   $251.40  
  7 purchase totals = $920.18       $1,004.5489   $1,004.56   $1,004.55   $1,004.40