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 $73.66   12.636%   $82.9677   $82.97   $82.95   $83.00  
  Purchase #2 $104.51   8.103%   $112.9784   $112.98   $113.00   $113.00  
  Purchase #3 $210.54   11.471%   $234.691   $234.69   $234.70   $234.70  
  Purchase #4 $106.79   8.386%   $115.7454   $115.75   $115.75   $115.70  
  Purchase #5 $181.96   12.690%   $205.0507   $205.05   $205.05   $205.10  
  Purchase #6 $237.73   8.823%   $258.7049   $258.70   $258.70   $258.70  
  Purchase #7 $22.65   12.133%   $25.3981   $25.40   $25.40   $25.40  
  7 purchase totals = $937.84       $1,035.5362   $1,035.54   $1,035.55   $1,035.60