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 $44.38   5.811%   $46.9589   $46.96   $46.95   $47.00  
  Purchase #2 $68.53   4.374%   $71.5275   $71.53   $71.55   $71.50  
  Purchase #3 $68.41   6.442%   $72.817   $72.82   $72.80   $72.80  
  Purchase #4 $63.79   10.752%   $70.6487   $70.65   $70.65   $70.60  
  Purchase #5 $128.75   12.774%   $145.1965   $145.20   $145.20   $145.20  
  Purchase #6 $173.65   9.413%   $189.9957   $190.00   $190.00   $190.00  
  Purchase #7 $69.74   12.365%   $78.3634   $78.36   $78.35   $78.40  
  7 purchase totals = $617.25       $675.5077   $675.52   $675.50   $675.50