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 $62.89   12.237%   $70.5858   $70.59   $70.60   $70.60  
  Purchase #2 $104.85   11.392%   $116.7945   $116.79   $116.80   $116.80  
  Purchase #3 $67.59   10.492%   $74.6815   $74.68   $74.70   $74.70  
  Purchase #4 $53.96   9.418%   $59.042   $59.04   $59.05   $59.00  
  Purchase #5 $225.27   12.752%   $253.9964   $254.00   $254.00   $254.00  
  Purchase #6 $180.79   12.740%   $203.8226   $203.82   $203.80   $203.80  
  Purchase #7 $157.43   4.243%   $164.1098   $164.11   $164.10   $164.10  
  7 purchase totals = $852.78       $943.0326   $943.03   $943.05   $943.00