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 $170.87   12.740%   $192.6388   $192.64   $192.65   $192.60  
  Purchase #2 $154.87   13.596%   $175.9261   $175.93   $175.95   $175.90  
  Purchase #3 $106.67   4.789%   $111.7784   $111.78   $111.80   $111.80  
  Purchase #4 $229.84   9.524%   $251.73   $251.73   $251.75   $251.70  
  Purchase #5 $65.37   9.758%   $71.7488   $71.75   $71.75   $71.70  
  Purchase #6 $64.62   5.205%   $67.9835   $67.98   $68.00   $68.00  
  Purchase #7 $146.62   9.656%   $160.7776   $160.78   $160.80   $160.80  
  7 purchase totals = $938.86       $1,032.5832   $1,032.59   $1,032.70   $1,032.50