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 $22.67   13.281%   $25.6808   $25.68   $25.70   $25.70  
  Purchase #2 $33.31   13.539%   $37.8198   $37.82   $37.80   $37.80  
  Purchase #3 $193.45   5.758%   $204.5889   $204.59   $204.60   $204.60  
  Purchase #4 $230.85   5.820%   $244.2855   $244.29   $244.30   $244.30  
  Purchase #5 $21.76   13.166%   $24.6249   $24.62   $24.60   $24.60  
  Purchase #6 $161.48   11.560%   $180.1471   $180.15   $180.15   $180.10  
  Purchase #7 $248.46   10.734%   $275.1297   $275.13   $275.15   $275.10  
  7 purchase totals = $911.98       $992.2767   $992.28   $992.30   $992.20