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 $184.77   10.248%   $203.7052   $203.71   $203.70   $203.70  
  Purchase #2 $90.55   6.377%   $96.3244   $96.32   $96.30   $96.30  
  Purchase #3 $45.39   11.622%   $50.6652   $50.67   $50.65   $50.70  
  Purchase #4 $212.30   5.667%   $224.331   $224.33   $224.35   $224.30  
  Purchase #5 $217.25   9.863%   $238.6774   $238.68   $238.70   $238.70  
  Purchase #6 $93.48   5.318%   $98.4513   $98.45   $98.45   $98.50  
  Purchase #7 $106.85   10.419%   $117.9827   $117.98   $118.00   $118.00  
  7 purchase totals = $950.59       $1,030.1372   $1,030.14   $1,030.15   $1,030.20