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 $97.56   5.187%   $102.6204   $102.62   $102.60   $102.60  
  Purchase #2 $226.89   8.199%   $245.4927   $245.49   $245.50   $245.50  
  Purchase #3 $111.50   13.472%   $126.5213   $126.52   $126.50   $126.50  
  Purchase #4 $240.31   9.676%   $263.5624   $263.56   $263.55   $263.60  
  Purchase #5 $223.26   13.102%   $252.5115   $252.51   $252.50   $252.50  
  Purchase #6 $21.92   12.586%   $24.6789   $24.68   $24.70   $24.70  
  Purchase #7 $55.93   5.424%   $58.9636   $58.96   $58.95   $59.00  
  7 purchase totals = $977.37       $1,074.3508   $1,074.34   $1,074.30   $1,074.40