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 $115.45   11.572%   $128.8099   $128.81   $128.80   $128.80  
  Purchase #2 $71.28   12.568%   $80.2385   $80.24   $80.25   $80.20  
  Purchase #3 $174.79   8.574%   $189.7765   $189.78   $189.80   $189.80  
  Purchase #4 $183.74   9.384%   $200.9822   $200.98   $201.00   $201.00  
  Purchase #5 $225.93   3.820%   $234.5605   $234.56   $234.55   $234.60  
  Purchase #6 $30.31   6.488%   $32.2765   $32.28   $32.30   $32.30  
  Purchase #7 $227.35   13.315%   $257.6217   $257.62   $257.60   $257.60  
  7 purchase totals = $1,028.85       $1,124.2658   $1,124.27   $1,124.30   $1,124.30