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 $230.83   10.189%   $254.3493   $254.35   $254.35   $254.30  
  Purchase #2 $34.82   5.437%   $36.7132   $36.71   $36.70   $36.70  
  Purchase #3 $58.48   6.315%   $62.173   $62.17   $62.15   $62.20  
  Purchase #4 $243.93   10.112%   $268.5962   $268.60   $268.60   $268.60  
  Purchase #5 $194.40   6.642%   $207.312   $207.31   $207.30   $207.30  
  Purchase #6 $98.48   6.566%   $104.9462   $104.95   $104.95   $104.90  
  Purchase #7 $193.55   4.407%   $202.0797   $202.08   $202.10   $202.10  
  7 purchase totals = $1,054.49       $1,136.1696   $1,136.17   $1,136.15   $1,136.10