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 $125.86   4.544%   $131.5791   $131.58   $131.60   $131.60  
  Purchase #2 $179.74   13.339%   $203.7155   $203.72   $203.70   $203.70  
  Purchase #3 $234.96   8.405%   $254.7084   $254.71   $254.70   $254.70  
  Purchase #4 $136.68   10.233%   $150.6665   $150.67   $150.65   $150.70  
  Purchase #5 $91.58   8.455%   $99.3231   $99.32   $99.30   $99.30  
  Purchase #6 $132.37   10.204%   $145.877   $145.88   $145.90   $145.90  
  Purchase #7 $223.99   11.764%   $250.3402   $250.34   $250.35   $250.30  
  7 purchase totals = $1,125.18       $1,236.2098   $1,236.22   $1,236.20   $1,236.20