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 $97.29   12.681%   $109.6273   $109.63   $109.65   $109.60  
  Purchase #2 $130.60   12.454%   $146.8649   $146.86   $146.85   $146.90  
  Purchase #3 $222.79   8.418%   $241.5445   $241.54   $241.55   $241.50  
  Purchase #4 $244.71   9.238%   $267.3163   $267.32   $267.30   $267.30  
  Purchase #5 $31.44   5.768%   $33.2535   $33.25   $33.25   $33.30  
  Purchase #6 $240.40   8.283%   $260.3123   $260.31   $260.30   $260.30  
  Purchase #7 $10.81   10.657%   $11.962   $11.96   $11.95   $12.00  
  7 purchase totals = $978.04       $1,070.8808   $1,070.87   $1,070.85   $1,070.90