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 $48.96   11.614%   $54.6462   $54.65   $54.65   $54.60  
  Purchase #2 $156.79   3.642%   $162.5003   $162.50   $162.50   $162.50  
  Purchase #3 $45.87   6.806%   $48.9919   $48.99   $49.00   $49.00  
  Purchase #4 $242.87   10.134%   $267.4824   $267.48   $267.50   $267.50  
  Purchase #5 $154.33   9.387%   $168.817   $168.82   $168.80   $168.80  
  Purchase #6 $246.46   11.713%   $275.3279   $275.33   $275.35   $275.30  
  Purchase #7 $23.52   12.185%   $26.3859   $26.39   $26.40   $26.40  
  7 purchase totals = $918.80       $1,004.1516   $1,004.16   $1,004.20   $1,004.10