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 $119.79   12.288%   $134.5098   $134.51   $134.50   $134.50  
  Purchase #2 $194.35   4.674%   $203.4339   $203.43   $203.45   $203.40  
  Purchase #3 $119.57   4.299%   $124.7103   $124.71   $124.70   $124.70  
  Purchase #4 $195.53   4.656%   $204.6339   $204.63   $204.65   $204.60  
  Purchase #5 $87.76   6.566%   $93.5223   $93.52   $93.50   $93.50  
  Purchase #6 $87.84   11.436%   $97.8854   $97.89   $97.90   $97.90  
  Purchase #7 $139.85   9.309%   $152.8686   $152.87   $152.85   $152.90  
  7 purchase totals = $944.69       $1,011.5642   $1,011.56   $1,011.55   $1,011.50