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 $57.83   6.576%   $61.6329   $61.63   $61.65   $61.60  
  Purchase #2 $155.31   9.593%   $170.2089   $170.21   $170.20   $170.20  
  Purchase #3 $28.58   6.791%   $30.5209   $30.52   $30.50   $30.50  
  Purchase #4 $219.84   8.467%   $238.4539   $238.45   $238.45   $238.50  
  Purchase #5 $218.43   3.192%   $225.4023   $225.40   $225.40   $225.40  
  Purchase #6 $193.28   6.404%   $205.6577   $205.66   $205.65   $205.70  
  Purchase #7 $21.61   5.372%   $22.7709   $22.77   $22.75   $22.80  
  7 purchase totals = $894.88       $954.6475   $954.64   $954.60   $954.70