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 $83.37   12.721%   $93.9755   $93.98   $94.00   $94.00  
  Purchase #2 $41.75   8.217%   $45.1806   $45.18   $45.20   $45.20  
  Purchase #3 $6.35   5.494%   $6.6989   $6.70   $6.70   $6.70  
  Purchase #4 $89.32   8.662%   $97.0569   $97.06   $97.05   $97.10  
  Purchase #5 $167.57   10.164%   $184.6018   $184.60   $184.60   $184.60  
  Purchase #6 $5.30   10.403%   $5.8514   $5.85   $5.85   $5.90  
  Purchase #7 $147.56   10.314%   $162.7793   $162.78   $162.80   $162.80  
  7 purchase totals = $541.22       $596.1444   $596.15   $596.20   $596.30