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 $46.65   13.114%   $52.7677   $52.77   $52.75   $52.80  
  Purchase #2 $222.71   9.856%   $244.6603   $244.66   $244.65   $244.70  
  Purchase #3 $102.48   8.862%   $111.5618   $111.56   $111.55   $111.60  
  Purchase #4 $181.43   6.274%   $192.8129   $192.81   $192.80   $192.80  
  Purchase #5 $150.29   4.327%   $156.793   $156.79   $156.80   $156.80  
  Purchase #6 $168.93   3.390%   $174.6567   $174.66   $174.65   $174.70  
  Purchase #7 $234.43   10.474%   $258.9842   $258.98   $259.00   $259.00  
  7 purchase totals = $1,106.92       $1,192.2366   $1,192.23   $1,192.20   $1,192.40