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 $162.44   11.689%   $181.4276   $181.43   $181.45   $181.40  
  Purchase #2 $227.90   9.840%   $250.3254   $250.33   $250.35   $250.30  
  Purchase #3 $44.40   11.226%   $49.3843   $49.38   $49.40   $49.40  
  Purchase #4 $203.94   10.736%   $225.835   $225.84   $225.85   $225.80  
  Purchase #5 $193.83   8.422%   $210.1544   $210.15   $210.15   $210.20  
  Purchase #6 $246.41   11.568%   $274.9147   $274.91   $274.90   $274.90  
  Purchase #7 $165.64   13.559%   $188.0991   $188.10   $188.10   $188.10  
  7 purchase totals = $1,244.56       $1,380.1405   $1,380.14   $1,380.20   $1,380.10