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 $208.90   9.272%   $228.2692   $228.27   $228.25   $228.30  
  Purchase #2 $169.95   13.367%   $192.6672   $192.67   $192.65   $192.70  
  Purchase #3 $149.26   13.650%   $169.634   $169.63   $169.65   $169.60  
  Purchase #4 $135.41   5.740%   $143.1825   $143.18   $143.20   $143.20  
  Purchase #5 $29.60   4.845%   $31.0341   $31.03   $31.05   $31.00  
  Purchase #6 $145.79   5.274%   $153.479   $153.48   $153.50   $153.50  
  Purchase #7 $106.66   9.184%   $116.4557   $116.46   $116.45   $116.50  
  7 purchase totals = $945.57       $1,034.7217   $1,034.72   $1,034.75   $1,034.80