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 $62.29   8.650%   $67.6781   $67.68   $67.70   $67.70  
  Purchase #2 $160.48   3.470%   $166.0487   $166.05   $166.05   $166.00  
  Purchase #3 $44.94   4.445%   $46.9376   $46.94   $46.95   $46.90  
  Purchase #4 $208.56   8.847%   $227.0113   $227.01   $227.00   $227.00  
  Purchase #5 $145.96   9.823%   $160.2977   $160.30   $160.30   $160.30  
  Purchase #6 $135.63   10.717%   $150.1655   $150.17   $150.15   $150.20  
  Purchase #7 $96.58   12.727%   $108.8717   $108.87   $108.85   $108.90  
  7 purchase totals = $854.44       $927.0106   $927.02   $927.00   $927.00