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 $140.86   4.788%   $147.6044   $147.60   $147.60   $147.60  
  Purchase #2 $233.57   9.613%   $256.0231   $256.02   $256.00   $256.00  
  Purchase #3 $200.80   10.551%   $221.9864   $221.99   $222.00   $222.00  
  Purchase #4 $203.27   3.210%   $209.795   $209.80   $209.80   $209.80  
  Purchase #5 $212.83   11.625%   $237.5715   $237.57   $237.55   $237.60  
  Purchase #6 $67.54   8.648%   $73.3809   $73.38   $73.40   $73.40  
  Purchase #7 $45.67   7.319%   $49.0126   $49.01   $49.00   $49.00  
  7 purchase totals = $1,104.54       $1,195.3739   $1,195.37   $1,195.35   $1,195.40