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 $84.86   12.221%   $95.2307   $95.23   $95.25   $95.20  
  Purchase #2 $6.47   9.831%   $7.1061   $7.11   $7.10   $7.10  
  Purchase #3 $36.74   11.158%   $40.8394   $40.84   $40.85   $40.80  
  Purchase #4 $206.79   6.753%   $220.7545   $220.75   $220.75   $220.80  
  Purchase #5 $51.82   12.200%   $58.142   $58.14   $58.15   $58.10  
  Purchase #6 $202.74   9.609%   $222.2213   $222.22   $222.20   $222.20  
  Purchase #7 $84.94   10.678%   $94.0099   $94.01   $94.00   $94.00  
  7 purchase totals = $674.36       $738.3039   $738.30   $738.30   $738.20