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 $11.67   3.252%   $12.0495   $12.05   $12.05   $12.00  
  Purchase #2 $219.40   10.219%   $241.8205   $241.82   $241.80   $241.80  
  Purchase #3 $100.50   9.150%   $109.6958   $109.70   $109.70   $109.70  
  Purchase #4 $147.84   5.415%   $155.8455   $155.85   $155.85   $155.80  
  Purchase #5 $237.71   5.726%   $251.3213   $251.32   $251.30   $251.30  
  Purchase #6 $195.36   7.130%   $209.2892   $209.29   $209.30   $209.30  
  Purchase #7 $45.58   11.700%   $50.9129   $50.91   $50.90   $50.90  
  7 purchase totals = $958.06       $1,030.9347   $1,030.94   $1,030.90   $1,030.80