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 $163.72   3.184%   $168.9328   $168.93   $168.95   $168.90  
  Purchase #2 $41.65   12.174%   $46.7205   $46.72   $46.70   $46.70  
  Purchase #3 $95.51   3.700%   $99.0439   $99.04   $99.05   $99.00  
  Purchase #4 $146.60   5.679%   $154.9254   $154.93   $154.95   $154.90  
  Purchase #5 $197.53   4.338%   $206.0989   $206.10   $206.10   $206.10  
  Purchase #6 $200.50   5.874%   $212.2774   $212.28   $212.30   $212.30  
  Purchase #7 $132.75   4.260%   $138.4052   $138.41   $138.40   $138.40  
  7 purchase totals = $978.26       $1,026.4041   $1,026.41   $1,026.45   $1,026.30