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 $244.95   9.121%   $267.2919   $267.29   $267.30   $267.30  
  Purchase #2 $5.89   3.777%   $6.1125   $6.11   $6.10   $6.10  
  Purchase #3 $146.80   11.642%   $163.8905   $163.89   $163.90   $163.90  
  Purchase #4 $128.77   5.358%   $135.6695   $135.67   $135.65   $135.70  
  Purchase #5 $8.54   3.868%   $8.8703   $8.87   $8.85   $8.90  
  Purchase #6 $156.35   6.287%   $166.1797   $166.18   $166.20   $166.20  
  Purchase #7 $201.92   4.414%   $210.8327   $210.83   $210.85   $210.80  
  7 purchase totals = $893.22       $958.8471   $958.84   $958.85   $958.90