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 $31.91   12.279%   $35.8282   $35.83   $35.85   $35.80  
  Purchase #2 $167.65   11.850%   $187.5165   $187.52   $187.50   $187.50  
  Purchase #3 $167.27   4.234%   $174.3522   $174.35   $174.35   $174.40  
  Purchase #4 $201.95   11.794%   $225.768   $225.77   $225.75   $225.80  
  Purchase #5 $82.71   8.647%   $89.8619   $89.86   $89.85   $89.90  
  Purchase #6 $232.47   6.731%   $248.1176   $248.12   $248.10   $248.10  
  Purchase #7 $75.34   11.776%   $84.212   $84.21   $84.20   $84.20  
  7 purchase totals = $959.30       $1,045.6564   $1,045.66   $1,045.60   $1,045.70