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 $69.70   7.598%   $74.9958   $75.00   $75.00   $75.00  
  Purchase #2 $112.40   12.109%   $126.0105   $126.01   $126.00   $126.00  
  Purchase #3 $172.91   4.715%   $181.0627   $181.06   $181.05   $181.10  
  Purchase #4 $91.98   9.307%   $100.5406   $100.54   $100.55   $100.50  
  Purchase #5 $121.60   8.370%   $131.7779   $131.78   $131.80   $131.80  
  Purchase #6 $120.67   10.569%   $133.4236   $133.42   $133.40   $133.40  
  Purchase #7 $223.92   9.331%   $244.814   $244.81   $244.80   $244.80  
  7 purchase totals = $913.18       $992.6251   $992.62   $992.60   $992.60