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 $54.69   3.469%   $56.5872   $56.59   $56.60   $56.60  
  Purchase #2 $124.38   8.470%   $134.915   $134.92   $134.90   $134.90  
  Purchase #3 $189.34   8.328%   $205.1082   $205.11   $205.10   $205.10  
  Purchase #4 $138.92   11.360%   $154.7013   $154.70   $154.70   $154.70  
  Purchase #5 $36.85   6.259%   $39.1564   $39.16   $39.15   $39.20  
  Purchase #6 $212.43   5.445%   $223.9968   $224.00   $224.00   $224.00  
  Purchase #7 $246.37   8.822%   $268.1048   $268.10   $268.10   $268.10  
  7 purchase totals = $1,002.98       $1,082.5697   $1,082.58   $1,082.55   $1,082.60