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 $123.68   13.818%   $140.7701   $140.77   $140.75   $140.80  
  Purchase #2 $134.32   12.117%   $150.5956   $150.60   $150.60   $150.60  
  Purchase #3 $221.29   9.241%   $241.7394   $241.74   $241.75   $241.70  
  Purchase #4 $236.82   13.677%   $269.2099   $269.21   $269.20   $269.20  
  Purchase #5 $196.43   11.729%   $219.4693   $219.47   $219.45   $219.50  
  Purchase #6 $120.53   3.154%   $124.3315   $124.33   $124.35   $124.30  
  Purchase #7 $46.96   10.785%   $52.0246   $52.02   $52.00   $52.00  
  7 purchase totals = $1,080.03       $1,198.1404   $1,198.14   $1,198.10   $1,198.10