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 $56.74   4.120%   $59.0777   $59.08   $59.10   $59.10  
  Purchase #2 $240.95   10.421%   $266.0594   $266.06   $266.05   $266.10  
  Purchase #3 $21.33   10.767%   $23.6266   $23.63   $23.65   $23.60  
  Purchase #4 $160.62   8.364%   $174.0543   $174.05   $174.05   $174.10  
  Purchase #5 $68.87   7.465%   $74.0111   $74.01   $74.00   $74.00  
  Purchase #6 $203.72   12.124%   $228.419   $228.42   $228.40   $228.40  
  Purchase #7 $11.89   12.499%   $13.3761   $13.38   $13.40   $13.40  
  7 purchase totals = $764.12       $838.6242   $838.63   $838.65   $838.70