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 $119.94   11.686%   $133.9562   $133.96   $133.95   $134.00  
  Purchase #2 $53.91   11.647%   $60.1889   $60.19   $60.20   $60.20  
  Purchase #3 $135.87   8.514%   $147.438   $147.44   $147.45   $147.40  
  Purchase #4 $181.26   13.414%   $205.5742   $205.57   $205.55   $205.60  
  Purchase #5 $207.76   7.518%   $223.3794   $223.38   $223.40   $223.40  
  Purchase #6 $132.69   13.326%   $150.3723   $150.37   $150.35   $150.40  
  Purchase #7 $141.98   13.466%   $161.099   $161.10   $161.10   $161.10  
  7 purchase totals = $973.41       $1,082.0080   $1,082.01   $1,082.00   $1,082.10