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 $64.89   5.834%   $68.6757   $68.68   $68.70   $68.70  
  Purchase #2 $201.65   4.617%   $210.9602   $210.96   $210.95   $211.00  
  Purchase #3 $162.37   8.563%   $176.2737   $176.27   $176.25   $176.30  
  Purchase #4 $191.64   9.363%   $209.5833   $209.58   $209.60   $209.60  
  Purchase #5 $203.57   11.549%   $227.0803   $227.08   $227.10   $227.10  
  Purchase #6 $146.40   6.604%   $156.0683   $156.07   $156.05   $156.10  
  Purchase #7 $106.41   10.444%   $117.5235   $117.52   $117.50   $117.50  
  7 purchase totals = $1,076.93       $1,166.1650   $1,166.16   $1,166.15   $1,166.30