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 $81.47   13.654%   $92.5939   $92.59   $92.60   $92.60  
  Purchase #2 $176.56   8.297%   $191.2092   $191.21   $191.20   $191.20  
  Purchase #3 $141.69   9.414%   $155.0287   $155.03   $155.05   $155.00  
  Purchase #4 $208.73   12.471%   $234.7607   $234.76   $234.75   $234.80  
  Purchase #5 $180.96   11.187%   $201.204   $201.20   $201.20   $201.20  
  Purchase #6 $137.41   6.211%   $145.9445   $145.94   $145.95   $145.90  
  Purchase #7 $149.79   7.570%   $161.1291   $161.13   $161.15   $161.10  
  7 purchase totals = $1,076.61       $1,181.8701   $1,181.86   $1,181.90   $1,181.80