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 $59.47   9.575%   $65.1643   $65.16   $65.15   $65.20  
  Purchase #2 $181.48   13.255%   $205.5352   $205.54   $205.55   $205.50  
  Purchase #3 $175.35   4.729%   $183.6423   $183.64   $183.65   $183.60  
  Purchase #4 $200.82   12.295%   $225.5108   $225.51   $225.50   $225.50  
  Purchase #5 $129.33   9.103%   $141.1029   $141.10   $141.10   $141.10  
  Purchase #6 $245.57   8.729%   $267.0058   $267.01   $267.00   $267.00  
  Purchase #7 $165.70   3.407%   $171.3454   $171.35   $171.35   $171.30  
  7 purchase totals = $1,157.72       $1,259.3067   $1,259.31   $1,259.30   $1,259.20