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 $125.98   6.482%   $134.146   $134.15   $134.15   $134.10  
  Purchase #2 $153.73   8.503%   $166.8017   $166.80   $166.80   $166.80  
  Purchase #3 $70.88   8.720%   $77.0607   $77.06   $77.05   $77.10  
  Purchase #4 $204.63   7.402%   $219.7767   $219.78   $219.80   $219.80  
  Purchase #5 $97.54   7.632%   $104.9843   $104.98   $105.00   $105.00  
  Purchase #6 $222.39   7.220%   $238.4466   $238.45   $238.45   $238.40  
  Purchase #7 $8.65   7.497%   $9.2985   $9.30   $9.30   $9.30  
  7 purchase totals = $883.80       $950.5145   $950.52   $950.55   $950.50