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 $75.96   12.718%   $85.6206   $85.62   $85.60   $85.60  
  Purchase #2 $192.74   5.750%   $203.8226   $203.82   $203.80   $203.80  
  Purchase #3 $211.92   12.617%   $238.6579   $238.66   $238.65   $238.70  
  Purchase #4 $124.74   5.425%   $131.5071   $131.51   $131.50   $131.50  
  Purchase #5 $171.69   9.482%   $187.9696   $187.97   $187.95   $188.00  
  Purchase #6 $211.65   11.408%   $235.795   $235.80   $235.80   $235.80  
  Purchase #7 $202.43   4.345%   $211.2256   $211.23   $211.25   $211.20  
  7 purchase totals = $1,191.13       $1,294.5984   $1,294.61   $1,294.55   $1,294.60