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 $237.42   11.866%   $265.5923   $265.59   $265.60   $265.60  
  Purchase #2 $26.98   6.254%   $28.6673   $28.67   $28.65   $28.70  
  Purchase #3 $113.64   8.745%   $123.5778   $123.58   $123.60   $123.60  
  Purchase #4 $167.64   6.445%   $178.4444   $178.44   $178.45   $178.40  
  Purchase #5 $243.78   5.265%   $256.615   $256.62   $256.60   $256.60  
  Purchase #6 $223.91   8.832%   $243.6857   $243.69   $243.70   $243.70  
  Purchase #7 $204.98   8.282%   $221.9564   $221.96   $221.95   $222.00  
  7 purchase totals = $1,218.35       $1,318.5389   $1,318.55   $1,318.55   $1,318.60