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 $55.46   7.386%   $59.5563   $59.56   $59.55   $59.60  
  Purchase #2 $98.52   7.662%   $106.0686   $106.07   $106.05   $106.10  
  Purchase #3 $216.84   6.467%   $230.863   $230.86   $230.85   $230.90  
  Purchase #4 $139.26   11.578%   $155.3835   $155.38   $155.40   $155.40  
  Purchase #5 $44.92   9.260%   $49.0796   $49.08   $49.10   $49.10  
  Purchase #6 $129.35   9.612%   $141.7831   $141.78   $141.80   $141.80  
  Purchase #7 $18.44   5.538%   $19.4612   $19.46   $19.45   $19.50  
  7 purchase totals = $702.79       $762.1953   $762.19   $762.20   $762.40