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 $148.97   5.203%   $156.7209   $156.72   $156.70   $156.70  
  Purchase #2 $243.41   5.107%   $255.8409   $255.84   $255.85   $255.80  
  Purchase #3 $188.64   11.799%   $210.8976   $210.90   $210.90   $210.90  
  Purchase #4 $43.99   5.542%   $46.4279   $46.43   $46.45   $46.40  
  Purchase #5 $194.80   7.714%   $209.8269   $209.83   $209.85   $209.80  
  Purchase #6 $94.94   9.685%   $104.1349   $104.13   $104.15   $104.10  
  Purchase #7 $191.43   10.660%   $211.8364   $211.84   $211.85   $211.80  
  7 purchase totals = $1,106.18       $1,195.6855   $1,195.69   $1,195.75   $1,195.50