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 $218.29   10.796%   $241.8566   $241.86   $241.85   $241.90  
  Purchase #2 $203.95   4.112%   $212.3364   $212.34   $212.35   $212.30  
  Purchase #3 $230.45   3.305%   $238.0664   $238.07   $238.05   $238.10  
  Purchase #4 $206.27   8.827%   $224.4775   $224.48   $224.50   $224.50  
  Purchase #5 $5.83   6.570%   $6.213   $6.21   $6.20   $6.20  
  Purchase #6 $54.44   6.565%   $58.014   $58.01   $58.00   $58.00  
  Purchase #7 $133.30   12.166%   $149.5173   $149.52   $149.50   $149.50  
  7 purchase totals = $1,052.53       $1,130.4812   $1,130.49   $1,130.45   $1,130.50