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 $91.29   4.700%   $95.5806   $95.58   $95.60   $95.60  
  Purchase #2 $223.91   12.834%   $252.6466   $252.65   $252.65   $252.60  
  Purchase #3 $21.79   8.762%   $23.6992   $23.70   $23.70   $23.70  
  Purchase #4 $35.80   7.321%   $38.4209   $38.42   $38.40   $38.40  
  Purchase #5 $194.64   6.674%   $207.6303   $207.63   $207.65   $207.60  
  Purchase #6 $6.57   7.415%   $7.0572   $7.06   $7.05   $7.10  
  Purchase #7 $243.97   11.398%   $271.7777   $271.78   $271.80   $271.80  
  7 purchase totals = $817.97       $896.8125   $896.82   $896.85   $896.80