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 $22.31   10.173%   $24.5796   $24.58   $24.60   $24.60  
  Purchase #2 $169.46   10.137%   $186.6382   $186.64   $186.65   $186.60  
  Purchase #3 $121.37   7.148%   $130.0455   $130.05   $130.05   $130.00  
  Purchase #4 $116.91   13.138%   $132.2696   $132.27   $132.25   $132.30  
  Purchase #5 $114.55   9.620%   $125.5697   $125.57   $125.55   $125.60  
  Purchase #6 $112.35   7.460%   $120.7313   $120.73   $120.75   $120.70  
  Purchase #7 $130.80   12.737%   $147.46   $147.46   $147.45   $147.50  
  7 purchase totals = $787.75       $867.2939   $867.30   $867.30   $867.30