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 $151.86   10.583%   $167.9313   $167.93   $167.95   $167.90  
  Purchase #2 $56.96   9.351%   $62.2863   $62.29   $62.30   $62.30  
  Purchase #3 $156.67   11.633%   $174.8954   $174.90   $174.90   $174.90  
  Purchase #4 $149.73   10.761%   $165.8424   $165.84   $165.85   $165.80  
  Purchase #5 $80.42   10.229%   $88.6462   $88.65   $88.65   $88.60  
  Purchase #6 $234.35   13.774%   $266.6294   $266.63   $266.65   $266.60  
  Purchase #7 $161.43   3.488%   $167.0607   $167.06   $167.05   $167.10  
  7 purchase totals = $991.42       $1,093.2917   $1,093.30   $1,093.35   $1,093.20