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 $114.54   4.732%   $119.96   $119.96   $119.95   $120.00  
  Purchase #2 $85.62   13.102%   $96.8379   $96.84   $96.85   $96.80  
  Purchase #3 $230.77   11.401%   $257.0801   $257.08   $257.10   $257.10  
  Purchase #4 $154.77   5.791%   $163.7327   $163.73   $163.75   $163.70  
  Purchase #5 $48.94   10.556%   $54.1061   $54.11   $54.10   $54.10  
  Purchase #6 $238.88   11.160%   $265.539   $265.54   $265.55   $265.50  
  Purchase #7 $83.25   10.560%   $92.0412   $92.04   $92.05   $92.00  
  7 purchase totals = $956.77       $1,049.2970   $1,049.30   $1,049.35   $1,049.20