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 $8.68   6.657%   $9.2578   $9.26   $9.25   $9.30  
  Purchase #2 $167.53   3.262%   $172.9948   $172.99   $173.00   $173.00  
  Purchase #3 $219.46   10.592%   $242.7052   $242.71   $242.70   $242.70  
  Purchase #4 $244.47   11.702%   $273.0779   $273.08   $273.10   $273.10  
  Purchase #5 $29.83   12.645%   $33.602   $33.60   $33.60   $33.60  
  Purchase #6 $88.48   9.486%   $96.8732   $96.87   $96.85   $96.90  
  Purchase #7 $212.57   5.220%   $223.6662   $223.67   $223.65   $223.70  
  7 purchase totals = $971.02       $1,052.1771   $1,052.18   $1,052.15   $1,052.30