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 $140.94   7.503%   $151.5147   $151.51   $151.50   $151.50  
  Purchase #2 $125.44   8.107%   $135.6094   $135.61   $135.60   $135.60  
  Purchase #3 $180.88   6.702%   $193.0026   $193.00   $193.00   $193.00  
  Purchase #4 $193.94   11.642%   $216.5185   $216.52   $216.50   $216.50  
  Purchase #5 $245.74   11.642%   $274.3491   $274.35   $274.35   $274.30  
  Purchase #6 $37.44   4.202%   $39.0132   $39.01   $39.00   $39.00  
  Purchase #7 $227.27   11.548%   $253.5151   $253.52   $253.50   $253.50  
  7 purchase totals = $1,151.65       $1,263.5226   $1,263.52   $1,263.45   $1,263.40