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 $91.67   3.698%   $95.06   $95.06   $95.05   $95.10  
  Purchase #2 $198.51   6.582%   $211.5759   $211.58   $211.60   $211.60  
  Purchase #3 $246.26   9.746%   $270.2605   $270.26   $270.25   $270.30  
  Purchase #4 $209.43   12.583%   $235.7826   $235.78   $235.80   $235.80  
  Purchase #5 $137.83   5.392%   $145.2618   $145.26   $145.25   $145.30  
  Purchase #6 $34.74   4.533%   $36.3148   $36.31   $36.30   $36.30  
  Purchase #7 $63.75   9.741%   $69.9599   $69.96   $69.95   $70.00  
  7 purchase totals = $982.19       $1,064.2155   $1,064.21   $1,064.20   $1,064.40