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 $184.48   12.398%   $207.3518   $207.35   $207.35   $207.40  
  Purchase #2 $80.70   12.809%   $91.0369   $91.04   $91.05   $91.00  
  Purchase #3 $173.28   11.769%   $193.6733   $193.67   $193.65   $193.70  
  Purchase #4 $128.52   8.591%   $139.5612   $139.56   $139.55   $139.60  
  Purchase #5 $15.42   13.525%   $17.5056   $17.51   $17.50   $17.50  
  Purchase #6 $185.42   8.625%   $201.4125   $201.41   $201.40   $201.40  
  Purchase #7 $186.63   12.407%   $209.7852   $209.79   $209.80   $209.80  
  7 purchase totals = $954.45       $1,060.3265   $1,060.33   $1,060.30   $1,060.40