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 $59.28   11.275%   $65.9638   $65.96   $65.95   $66.00  
  Purchase #2 $217.92   4.758%   $228.2886   $228.29   $228.30   $228.30  
  Purchase #3 $215.77   12.529%   $242.8038   $242.80   $242.80   $242.80  
  Purchase #4 $126.39   6.226%   $134.259   $134.26   $134.25   $134.30  
  Purchase #5 $202.64   6.580%   $215.9737   $215.97   $215.95   $216.00  
  Purchase #6 $49.31   11.779%   $55.1182   $55.12   $55.10   $55.10  
  Purchase #7 $219.37   9.698%   $240.6445   $240.64   $240.65   $240.60  
  7 purchase totals = $1,090.68       $1,183.0516   $1,183.04   $1,183.00   $1,183.10