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 $84.97   10.445%   $93.8451   $93.85   $93.85   $93.80  
  Purchase #2 $54.81   9.195%   $59.8498   $59.85   $59.85   $59.80  
  Purchase #3 $79.45   11.231%   $88.373   $88.37   $88.35   $88.40  
  Purchase #4 $231.98   3.721%   $240.612   $240.61   $240.60   $240.60  
  Purchase #5 $37.87   3.363%   $39.1436   $39.14   $39.15   $39.10  
  Purchase #6 $55.66   13.659%   $63.2626   $63.26   $63.25   $63.30  
  Purchase #7 $228.92   13.665%   $260.2019   $260.20   $260.20   $260.20  
  7 purchase totals = $773.66       $845.2880   $845.28   $845.25   $845.20