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 $187.97   8.102%   $203.1993   $203.20   $203.20   $203.20  
  Purchase #2 $192.77   10.414%   $212.8451   $212.85   $212.85   $212.80  
  Purchase #3 $108.98   8.256%   $117.9774   $117.98   $118.00   $118.00  
  Purchase #4 $76.45   9.393%   $83.6309   $83.63   $83.65   $83.60  
  Purchase #5 $211.58   11.486%   $235.8821   $235.88   $235.90   $235.90  
  Purchase #6 $24.52   7.586%   $26.3801   $26.38   $26.40   $26.40  
  Purchase #7 $114.90   13.446%   $130.3495   $130.35   $130.35   $130.30  
  7 purchase totals = $917.17       $1,010.2644   $1,010.27   $1,010.35   $1,010.20