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 $164.60   11.654%   $183.7825   $183.78   $183.80   $183.80  
  Purchase #2 $143.42   4.472%   $149.8337   $149.83   $149.85   $149.80  
  Purchase #3 $162.26   8.753%   $176.4626   $176.46   $176.45   $176.50  
  Purchase #4 $242.52   7.413%   $260.498   $260.50   $260.50   $260.50  
  Purchase #5 $43.46   7.460%   $46.7021   $46.70   $46.70   $46.70  
  Purchase #6 $103.57   12.370%   $116.3816   $116.38   $116.40   $116.40  
  Purchase #7 $151.94   12.205%   $170.4843   $170.48   $170.50   $170.50  
  7 purchase totals = $1,011.77       $1,104.1448   $1,104.13   $1,104.20   $1,104.20