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 $84.44   11.122%   $93.8314   $93.83   $93.85   $93.80  
  Purchase #2 $54.48   10.748%   $60.3355   $60.34   $60.35   $60.30  
  Purchase #3 $91.32   3.146%   $94.1929   $94.19   $94.20   $94.20  
  Purchase #4 $137.26   13.404%   $155.6583   $155.66   $155.65   $155.70  
  Purchase #5 $26.31   4.318%   $27.4461   $27.45   $27.45   $27.40  
  Purchase #6 $213.74   11.840%   $239.0468   $239.05   $239.05   $239.00  
  Purchase #7 $22.65   11.386%   $25.2289   $25.23   $25.25   $25.20  
  7 purchase totals = $630.20       $695.7399   $695.75   $695.80   $695.60