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 $227.92   6.115%   $241.8573   $241.86   $241.85   $241.90  
  Purchase #2 $205.60   11.707%   $229.6696   $229.67   $229.65   $229.70  
  Purchase #3 $49.62   6.117%   $52.6553   $52.66   $52.65   $52.70  
  Purchase #4 $90.42   6.332%   $96.1454   $96.15   $96.15   $96.10  
  Purchase #5 $81.89   5.362%   $86.2809   $86.28   $86.30   $86.30  
  Purchase #6 $241.76   11.252%   $268.9628   $268.96   $268.95   $269.00  
  Purchase #7 $205.42   8.112%   $222.0837   $222.08   $222.10   $222.10  
  7 purchase totals = $1,102.63       $1,197.6550   $1,197.66   $1,197.65   $1,197.80