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 $190.88   10.869%   $211.6267   $211.63   $211.65   $211.60  
  Purchase #2 $48.73   13.485%   $55.3012   $55.30   $55.30   $55.30  
  Purchase #3 $75.85   10.351%   $83.7012   $83.70   $83.70   $83.70  
  Purchase #4 $229.31   6.336%   $243.8391   $243.84   $243.85   $243.80  
  Purchase #5 $140.64   10.310%   $155.14   $155.14   $155.15   $155.10  
  Purchase #6 $52.56   7.522%   $56.5136   $56.51   $56.50   $56.50  
  Purchase #7 $235.96   8.775%   $256.6655   $256.67   $256.65   $256.70  
  7 purchase totals = $973.93       $1,062.7873   $1,062.79   $1,062.80   $1,062.70