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 $216.67   8.579%   $235.2581   $235.26   $235.25   $235.30  
  Purchase #2 $209.84   12.804%   $236.7079   $236.71   $236.70   $236.70  
  Purchase #3 $115.29   12.850%   $130.1048   $130.10   $130.10   $130.10  
  Purchase #4 $87.87   3.311%   $90.7794   $90.78   $90.80   $90.80  
  Purchase #5 $80.47   10.581%   $88.9845   $88.98   $89.00   $89.00  
  Purchase #6 $126.89   8.593%   $137.7937   $137.79   $137.80   $137.80  
  Purchase #7 $128.88   7.508%   $138.5563   $138.56   $138.55   $138.60  
  7 purchase totals = $965.91       $1,058.1847   $1,058.18   $1,058.20   $1,058.30