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 $88.26   6.749%   $94.2167   $94.22   $94.20   $94.20  
  Purchase #2 $139.31   9.562%   $152.6308   $152.63   $152.65   $152.60  
  Purchase #3 $236.94   12.726%   $267.093   $267.09   $267.10   $267.10  
  Purchase #4 $203.94   11.573%   $227.542   $227.54   $227.55   $227.50  
  Purchase #5 $21.90   13.447%   $24.8449   $24.84   $24.85   $24.80  
  Purchase #6 $93.25   11.275%   $103.7639   $103.76   $103.75   $103.80  
  Purchase #7 $187.99   9.476%   $205.8039   $205.80   $205.80   $205.80  
  7 purchase totals = $971.59       $1,075.8952   $1,075.88   $1,075.90   $1,075.80