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 $233.32   8.392%   $252.9002   $252.90   $252.90   $252.90  
  Purchase #2 $53.42   8.698%   $58.0665   $58.07   $58.05   $58.10  
  Purchase #3 $123.52   9.148%   $134.8196   $134.82   $134.80   $134.80  
  Purchase #4 $172.43   6.305%   $183.3017   $183.30   $183.30   $183.30  
  Purchase #5 $161.35   8.568%   $175.1745   $175.17   $175.15   $175.20  
  Purchase #6 $185.53   10.113%   $204.2926   $204.29   $204.30   $204.30  
  Purchase #7 $181.72   13.419%   $206.105   $206.11   $206.10   $206.10  
  7 purchase totals = $1,111.29       $1,214.6601   $1,214.66   $1,214.60   $1,214.70