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 $91.48   5.264%   $96.2955   $96.30   $96.30   $96.30  
  Purchase #2 $203.94   3.244%   $210.5558   $210.56   $210.55   $210.60  
  Purchase #3 $202.39   8.161%   $218.907   $218.91   $218.90   $218.90  
  Purchase #4 $121.97   5.220%   $128.3368   $128.34   $128.35   $128.30  
  Purchase #5 $124.72   7.681%   $134.2997   $134.30   $134.30   $134.30  
  Purchase #6 $19.32   7.752%   $20.8177   $20.82   $20.80   $20.80  
  Purchase #7 $145.96   8.428%   $158.2615   $158.26   $158.25   $158.30  
  7 purchase totals = $909.78       $967.4740   $967.49   $967.45   $967.50