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 $32.31   9.194%   $35.2806   $35.28   $35.30   $35.30  
  Purchase #2 $246.38   4.537%   $257.5583   $257.56   $257.55   $257.60  
  Purchase #3 $19.85   11.377%   $22.1083   $22.11   $22.10   $22.10  
  Purchase #4 $117.62   3.130%   $121.3015   $121.30   $121.30   $121.30  
  Purchase #5 $56.86   8.145%   $61.4912   $61.49   $61.50   $61.50  
  Purchase #6 $162.47   4.818%   $170.2978   $170.30   $170.30   $170.30  
  Purchase #7 $56.41   12.753%   $63.604   $63.60   $63.60   $63.60  
  7 purchase totals = $691.90       $731.6417   $731.64   $731.65   $731.70