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 $53.77   8.433%   $58.3044   $58.30   $58.30   $58.30  
  Purchase #2 $201.25   9.237%   $219.8395   $219.84   $219.85   $219.80  
  Purchase #3 $43.68   5.708%   $46.1733   $46.17   $46.15   $46.20  
  Purchase #4 $213.32   13.667%   $242.4744   $242.47   $242.45   $242.50  
  Purchase #5 $201.47   7.739%   $217.0618   $217.06   $217.05   $217.10  
  Purchase #6 $21.33   5.115%   $22.421   $22.42   $22.40   $22.40  
  Purchase #7 $225.94   6.816%   $241.3401   $241.34   $241.35   $241.30  
  7 purchase totals = $960.76       $1,047.6145   $1,047.60   $1,047.55   $1,047.60