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 $84.97   12.599%   $95.6754   $95.68   $95.70   $95.70  
  Purchase #2 $27.72   13.573%   $31.4824   $31.48   $31.50   $31.50  
  Purchase #3 $87.45   5.498%   $92.258   $92.26   $92.25   $92.30  
  Purchase #4 $248.82   6.293%   $264.4782   $264.48   $264.50   $264.50  
  Purchase #5 $244.58   13.511%   $277.6252   $277.63   $277.65   $277.60  
  Purchase #6 $189.56   7.770%   $204.2888   $204.29   $204.30   $204.30  
  Purchase #7 $223.82   6.792%   $239.0219   $239.02   $239.00   $239.00  
  7 purchase totals = $1,106.92       $1,204.8299   $1,204.84   $1,204.90   $1,204.90