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 $54.31   3.371%   $56.1408   $56.14   $56.15   $56.10  
  Purchase #2 $241.37   12.327%   $271.1237   $271.12   $271.10   $271.10  
  Purchase #3 $188.94   7.149%   $202.4473   $202.45   $202.45   $202.40  
  Purchase #4 $59.29   4.246%   $61.8075   $61.81   $61.80   $61.80  
  Purchase #5 $162.79   4.652%   $170.363   $170.36   $170.35   $170.40  
  Purchase #6 $82.68   8.657%   $89.8376   $89.84   $89.85   $89.80  
  Purchase #7 $62.68   13.206%   $70.9575   $70.96   $70.95   $71.00  
  7 purchase totals = $852.06       $922.6774   $922.68   $922.65   $922.60