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 $240.56   8.140%   $260.1416   $260.14   $260.15   $260.10  
  Purchase #2 $211.92   9.561%   $232.1817   $232.18   $232.20   $232.20  
  Purchase #3 $171.49   8.195%   $185.5436   $185.54   $185.55   $185.50  
  Purchase #4 $216.87   5.488%   $228.7718   $228.77   $228.75   $228.80  
  Purchase #5 $37.92   9.667%   $41.5857   $41.59   $41.60   $41.60  
  Purchase #6 $30.57   11.254%   $34.0103   $34.01   $34.00   $34.00  
  Purchase #7 $62.93   12.838%   $71.009   $71.01   $71.00   $71.00  
  7 purchase totals = $972.26       $1,053.2437   $1,053.24   $1,053.25   $1,053.20