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 $41.84   7.110%   $44.8148   $44.81   $44.80   $44.80  
  Purchase #2 $230.78   12.363%   $259.3113   $259.31   $259.30   $259.30  
  Purchase #3 $120.42   11.836%   $134.6729   $134.67   $134.65   $134.70  
  Purchase #4 $230.70   9.503%   $252.6234   $252.62   $252.60   $252.60  
  Purchase #5 $162.98   5.629%   $172.1541   $172.15   $172.15   $172.20  
  Purchase #6 $101.89   6.453%   $108.465   $108.47   $108.45   $108.50  
  Purchase #7 $60.78   6.645%   $64.8188   $64.82   $64.80   $64.80  
  7 purchase totals = $949.39       $1,036.8603   $1,036.85   $1,036.75   $1,036.90