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 $83.86   9.700%   $91.9944   $91.99   $92.00   $92.00  
  Purchase #2 $110.36   12.682%   $124.3559   $124.36   $124.35   $124.40  
  Purchase #3 $52.72   11.518%   $58.7923   $58.79   $58.80   $58.80  
  Purchase #4 $65.62   10.485%   $72.5003   $72.50   $72.50   $72.50  
  Purchase #5 $240.59   4.681%   $251.852   $251.85   $251.85   $251.90  
  Purchase #6 $189.55   6.773%   $202.3882   $202.39   $202.40   $202.40  
  Purchase #7 $179.77   8.745%   $195.4909   $195.49   $195.50   $195.50  
  7 purchase totals = $922.47       $997.3740   $997.37   $997.40   $997.50