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 $153.67   7.852%   $165.7362   $165.74   $165.75   $165.70  
  Purchase #2 $29.49   7.833%   $31.8   $31.80   $31.80   $31.80  
  Purchase #3 $10.61   6.263%   $11.2745   $11.27   $11.25   $11.30  
  Purchase #4 $222.56   7.483%   $239.2142   $239.21   $239.20   $239.20  
  Purchase #5 $54.29   10.417%   $59.9454   $59.95   $59.95   $59.90  
  Purchase #6 $44.76   9.816%   $49.1536   $49.15   $49.15   $49.20  
  Purchase #7 $180.61   8.826%   $196.5506   $196.55   $196.55   $196.60  
  7 purchase totals = $695.99       $753.6745   $753.67   $753.65   $753.70