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 $231.69   8.568%   $251.5412   $251.54   $251.55   $251.50  
  Purchase #2 $174.55   10.388%   $192.6823   $192.68   $192.70   $192.70  
  Purchase #3 $55.26   6.772%   $59.0022   $59.00   $59.00   $59.00  
  Purchase #4 $9.98   12.850%   $11.2624   $11.26   $11.25   $11.30  
  Purchase #5 $121.70   6.323%   $129.3951   $129.40   $129.40   $129.40  
  Purchase #6 $202.72   12.779%   $228.6256   $228.63   $228.65   $228.60  
  Purchase #7 $116.27   7.753%   $125.2844   $125.28   $125.30   $125.30  
  7 purchase totals = $912.17       $997.7932   $997.79   $997.85   $997.80