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 $83.41   13.367%   $94.5594   $94.56   $94.55   $94.60  
  Purchase #2 $10.51   5.137%   $11.0499   $11.05   $11.05   $11.00  
  Purchase #3 $74.43   13.755%   $84.6678   $84.67   $84.65   $84.70  
  Purchase #4 $64.84   6.757%   $69.2212   $69.22   $69.20   $69.20  
  Purchase #5 $155.88   8.211%   $168.6793   $168.68   $168.70   $168.70  
  Purchase #6 $181.48   11.406%   $202.1796   $202.18   $202.20   $202.20  
  Purchase #7 $165.82   4.279%   $172.9154   $172.92   $172.90   $172.90  
  7 purchase totals = $736.37       $803.2726   $803.28   $803.25   $803.30