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 $183.62   12.711%   $206.9599   $206.96   $206.95   $207.00  
  Purchase #2 $234.47   8.616%   $254.6719   $254.67   $254.65   $254.70  
  Purchase #3 $199.90   5.257%   $210.4087   $210.41   $210.40   $210.40  
  Purchase #4 $168.68   7.278%   $180.9565   $180.96   $180.95   $181.00  
  Purchase #5 $232.74   9.473%   $254.7875   $254.79   $254.80   $254.80  
  Purchase #6 $62.76   3.607%   $65.0238   $65.02   $65.00   $65.00  
  Purchase #7 $43.43   8.666%   $47.1936   $47.19   $47.20   $47.20  
  7 purchase totals = $1,125.60       $1,220.0019   $1,220.00   $1,219.95   $1,220.10