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 $173.68   12.387%   $195.1937   $195.19   $195.20   $195.20  
  Purchase #2 $246.95   11.453%   $275.2332   $275.23   $275.25   $275.20  
  Purchase #3 $211.82   12.349%   $237.9777   $237.98   $238.00   $238.00  
  Purchase #4 $54.68   4.241%   $56.999   $57.00   $57.00   $57.00  
  Purchase #5 $203.74   9.421%   $222.9343   $222.93   $222.95   $222.90  
  Purchase #6 $214.94   3.121%   $221.6483   $221.65   $221.65   $221.60  
  Purchase #7 $79.27   13.200%   $89.7336   $89.73   $89.75   $89.70  
  7 purchase totals = $1,185.08       $1,299.7198   $1,299.71   $1,299.80   $1,299.60