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 $91.36   6.112%   $96.9439   $96.94   $96.95   $96.90  
  Purchase #2 $216.92   13.104%   $245.3452   $245.35   $245.35   $245.30  
  Purchase #3 $67.62   8.604%   $73.438   $73.44   $73.45   $73.40  
  Purchase #4 $51.49   3.640%   $53.3642   $53.36   $53.35   $53.40  
  Purchase #5 $120.95   13.510%   $137.2903   $137.29   $137.30   $137.30  
  Purchase #6 $240.60   5.246%   $253.2219   $253.22   $253.20   $253.20  
  Purchase #7 $126.25   11.443%   $140.6968   $140.70   $140.70   $140.70  
  7 purchase totals = $915.19       $1,000.3003   $1,000.30   $1,000.30   $1,000.20