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 $58.26   10.285%   $64.252   $64.25   $64.25   $64.30  
  Purchase #2 $178.79   8.357%   $193.7315   $193.73   $193.75   $193.70  
  Purchase #3 $113.40   4.134%   $118.088   $118.09   $118.10   $118.10  
  Purchase #4 $227.63   12.804%   $256.7757   $256.78   $256.80   $256.80  
  Purchase #5 $173.52   12.850%   $195.8173   $195.82   $195.80   $195.80  
  Purchase #6 $212.50   4.701%   $222.4896   $222.49   $222.50   $222.50  
  Purchase #7 $124.84   8.621%   $135.6025   $135.60   $135.60   $135.60  
  7 purchase totals = $1,088.94       $1,186.7566   $1,186.76   $1,186.80   $1,186.80