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 $40.95   6.604%   $43.6543   $43.65   $43.65   $43.70  
  Purchase #2 $228.43   13.493%   $259.2521   $259.25   $259.25   $259.30  
  Purchase #3 $155.60   12.665%   $175.3067   $175.31   $175.30   $175.30  
  Purchase #4 $227.79   12.632%   $256.5644   $256.56   $256.55   $256.60  
  Purchase #5 $218.29   9.334%   $238.6652   $238.67   $238.65   $238.70  
  Purchase #6 $68.84   6.349%   $73.2107   $73.21   $73.20   $73.20  
  Purchase #7 $222.68   13.374%   $252.4612   $252.46   $252.45   $252.50  
  7 purchase totals = $1,162.58       $1,299.1146   $1,299.11   $1,299.05   $1,299.30