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 $168.84   7.454%   $181.4253   $181.43   $181.45   $181.40  
  Purchase #2 $139.55   8.561%   $151.4969   $151.50   $151.50   $151.50  
  Purchase #3 $98.83   5.708%   $104.4712   $104.47   $104.45   $104.50  
  Purchase #4 $176.27   6.192%   $187.1846   $187.18   $187.20   $187.20  
  Purchase #5 $248.42   11.804%   $277.7435   $277.74   $277.75   $277.70  
  Purchase #6 $40.67   7.135%   $43.5718   $43.57   $43.55   $43.60  
  Purchase #7 $72.98   6.570%   $77.7748   $77.77   $77.75   $77.80  
  7 purchase totals = $945.56       $1,023.6681   $1,023.66   $1,023.65   $1,023.70