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 $223.57   5.830%   $236.6041   $236.60   $236.60   $236.60  
  Purchase #2 $168.79   13.137%   $190.9639   $190.96   $190.95   $191.00  
  Purchase #3 $51.30   9.398%   $56.1212   $56.12   $56.10   $56.10  
  Purchase #4 $84.49   13.430%   $95.837   $95.84   $95.85   $95.80  
  Purchase #5 $18.36   9.532%   $20.1101   $20.11   $20.10   $20.10  
  Purchase #6 $232.32   6.727%   $247.9482   $247.95   $247.95   $247.90  
  Purchase #7 $196.62   3.419%   $203.3424   $203.34   $203.35   $203.30  
  7 purchase totals = $975.45       $1,050.9269   $1,050.92   $1,050.90   $1,050.80