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 $170.69   10.775%   $189.0818   $189.08   $189.10   $189.10  
  Purchase #2 $159.31   4.629%   $166.6845   $166.68   $166.70   $166.70  
  Purchase #3 $109.86   12.288%   $123.3596   $123.36   $123.35   $123.40  
  Purchase #4 $18.90   7.689%   $20.3532   $20.35   $20.35   $20.40  
  Purchase #5 $22.39   4.558%   $23.4105   $23.41   $23.40   $23.40  
  Purchase #6 $118.57   4.340%   $123.7159   $123.72   $123.70   $123.70  
  Purchase #7 $43.60   11.779%   $48.7356   $48.74   $48.75   $48.70  
  7 purchase totals = $643.32       $695.3411   $695.34   $695.35   $695.40