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 $169.54   8.735%   $184.3493   $184.35   $184.35   $184.30  
  Purchase #2 $69.53   11.157%   $77.2875   $77.29   $77.30   $77.30  
  Purchase #3 $116.96   13.528%   $132.7823   $132.78   $132.80   $132.80  
  Purchase #4 $134.47   6.871%   $143.7094   $143.71   $143.70   $143.70  
  Purchase #5 $169.54   13.503%   $192.433   $192.43   $192.45   $192.40  
  Purchase #6 $244.68   12.761%   $275.9036   $275.90   $275.90   $275.90  
  Purchase #7 $43.90   9.803%   $48.2035   $48.20   $48.20   $48.20  
  7 purchase totals = $948.62       $1,054.6686   $1,054.66   $1,054.70   $1,054.60