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 $211.41   11.412%   $235.5361   $235.54   $235.55   $235.50  
  Purchase #2 $77.73   6.176%   $82.5306   $82.53   $82.55   $82.50  
  Purchase #3 $191.33   6.443%   $203.6574   $203.66   $203.65   $203.70  
  Purchase #4 $236.47   6.107%   $250.9112   $250.91   $250.90   $250.90  
  Purchase #5 $181.69   10.813%   $201.3361   $201.34   $201.35   $201.30  
  Purchase #6 $103.68   3.382%   $107.1865   $107.19   $107.20   $107.20  
  Purchase #7 $25.52   13.353%   $28.9277   $28.93   $28.95   $28.90  
  7 purchase totals = $1,027.83       $1,110.0856   $1,110.10   $1,110.15   $1,110.00