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 $233.65   13.240%   $264.5853   $264.59   $264.60   $264.60  
  Purchase #2 $207.79   13.228%   $235.2765   $235.28   $235.30   $235.30  
  Purchase #3 $148.66   11.642%   $165.967   $165.97   $165.95   $166.00  
  Purchase #4 $43.75   8.267%   $47.3668   $47.37   $47.35   $47.40  
  Purchase #5 $202.70   11.168%   $225.3375   $225.34   $225.35   $225.30  
  Purchase #6 $126.47   9.729%   $138.7743   $138.77   $138.75   $138.80  
  Purchase #7 $16.44   7.220%   $17.627   $17.63   $17.65   $17.60  
  7 purchase totals = $979.46       $1,094.9344   $1,094.95   $1,094.95   $1,095.00