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 $191.81   13.663%   $218.017   $218.02   $218.00   $218.00  
  Purchase #2 $172.29   13.208%   $195.0461   $195.05   $195.05   $195.00  
  Purchase #3 $199.76   6.139%   $212.0233   $212.02   $212.00   $212.00  
  Purchase #4 $127.35   7.642%   $137.0821   $137.08   $137.10   $137.10  
  Purchase #5 $167.74   4.688%   $175.6037   $175.60   $175.60   $175.60  
  Purchase #6 $207.35   6.424%   $220.6702   $220.67   $220.65   $220.70  
  Purchase #7 $209.95   8.739%   $228.2975   $228.30   $228.30   $228.30  
  7 purchase totals = $1,276.25       $1,386.7399   $1,386.74   $1,386.70   $1,386.70