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 $85.54   10.274%   $94.3284   $94.33   $94.35   $94.30  
  Purchase #2 $80.48   6.194%   $85.4649   $85.46   $85.45   $85.50  
  Purchase #3 $119.51   3.425%   $123.6032   $123.60   $123.60   $123.60  
  Purchase #4 $216.74   8.698%   $235.592   $235.59   $235.60   $235.60  
  Purchase #5 $166.50   10.766%   $184.4254   $184.43   $184.45   $184.40  
  Purchase #6 $121.60   6.641%   $129.6755   $129.68   $129.70   $129.70  
  Purchase #7 $57.64   12.164%   $64.6513   $64.65   $64.65   $64.70  
  7 purchase totals = $848.01       $917.7407   $917.74   $917.80   $917.80