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 $94.79   10.262%   $104.5173   $104.52   $104.50   $104.50  
  Purchase #2 $232.87   4.321%   $242.9323   $242.93   $242.95   $242.90  
  Purchase #3 $212.93   11.130%   $236.6291   $236.63   $236.65   $236.60  
  Purchase #4 $189.42   3.132%   $195.3526   $195.35   $195.35   $195.40  
  Purchase #5 $85.89   9.523%   $94.0693   $94.07   $94.05   $94.10  
  Purchase #6 $219.64   5.322%   $231.3292   $231.33   $231.35   $231.30  
  Purchase #7 $183.47   10.423%   $202.5931   $202.59   $202.60   $202.60  
  7 purchase totals = $1,219.01       $1,307.4229   $1,307.42   $1,307.45   $1,307.40