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 $106.90   3.657%   $110.8093   $110.81   $110.80   $110.80  
  Purchase #2 $43.64   8.405%   $47.3079   $47.31   $47.30   $47.30  
  Purchase #3 $20.63   4.864%   $21.6334   $21.63   $21.65   $21.60  
  Purchase #4 $38.68   8.519%   $41.9751   $41.98   $42.00   $42.00  
  Purchase #5 $155.80   12.444%   $175.1878   $175.19   $175.20   $175.20  
  Purchase #6 $24.62   13.871%   $28.035   $28.04   $28.05   $28.00  
  Purchase #7 $200.47   10.111%   $220.7395   $220.74   $220.75   $220.70  
  7 purchase totals = $590.74       $645.6880   $645.70   $645.75   $645.60