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 $43.86   12.341%   $49.2728   $49.27   $49.25   $49.30  
  Purchase #2 $238.60   5.706%   $252.2145   $252.21   $252.20   $252.20  
  Purchase #3 $10.41   5.739%   $11.0074   $11.01   $11.00   $11.00  
  Purchase #4 $56.99   6.638%   $60.773   $60.77   $60.75   $60.80  
  Purchase #5 $118.29   9.417%   $129.4294   $129.43   $129.45   $129.40  
  Purchase #6 $203.39   12.292%   $228.3907   $228.39   $228.40   $228.40  
  Purchase #7 $161.33   5.503%   $170.208   $170.21   $170.20   $170.20  
  7 purchase totals = $832.87       $901.2958   $901.29   $901.25   $901.30