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 $47.31   11.465%   $52.7341   $52.73   $52.75   $52.70  
  Purchase #2 $247.47   13.216%   $280.1756   $280.18   $280.20   $280.20  
  Purchase #3 $223.74   8.841%   $243.5209   $243.52   $243.50   $243.50  
  Purchase #4 $142.62   10.216%   $157.1901   $157.19   $157.20   $157.20  
  Purchase #5 $133.37   8.416%   $144.5944   $144.59   $144.60   $144.60  
  Purchase #6 $112.55   4.301%   $117.3908   $117.39   $117.40   $117.40  
  Purchase #7 $23.61   5.706%   $24.9572   $24.96   $24.95   $25.00  
  7 purchase totals = $930.67       $1,020.5631   $1,020.56   $1,020.60   $1,020.60