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 $189.67   7.836%   $204.5325   $204.53   $204.55   $204.50  
  Purchase #2 $184.95   10.785%   $204.8969   $204.90   $204.90   $204.90  
  Purchase #3 $10.80   10.654%   $11.9506   $11.95   $11.95   $12.00  
  Purchase #4 $120.82   4.486%   $126.24   $126.24   $126.25   $126.20  
  Purchase #5 $96.57   8.441%   $104.7215   $104.72   $104.70   $104.70  
  Purchase #6 $224.74   4.212%   $234.206   $234.21   $234.20   $234.20  
  Purchase #7 $168.89   4.599%   $176.6573   $176.66   $176.65   $176.70  
  7 purchase totals = $996.44       $1,063.2048   $1,063.21   $1,063.20   $1,063.20