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 $238.65   12.614%   $268.7533   $268.75   $268.75   $268.80  
  Purchase #2 $189.38   3.434%   $195.8833   $195.88   $195.90   $195.90  
  Purchase #3 $164.45   13.301%   $186.3235   $186.32   $186.30   $186.30  
  Purchase #4 $173.89   4.132%   $181.0751   $181.08   $181.10   $181.10  
  Purchase #5 $230.45   9.164%   $251.5684   $251.57   $251.55   $251.60  
  Purchase #6 $66.38   12.322%   $74.5593   $74.56   $74.55   $74.60  
  Purchase #7 $30.61   11.657%   $34.1782   $34.18   $34.20   $34.20  
  7 purchase totals = $1,093.81       $1,192.3411   $1,192.34   $1,192.35   $1,192.50