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 $91.52   12.509%   $102.9682   $102.97   $102.95   $103.00  
  Purchase #2 $123.91   11.531%   $138.1981   $138.20   $138.20   $138.20  
  Purchase #3 $91.71   3.547%   $94.963   $94.96   $94.95   $95.00  
  Purchase #4 $39.31   3.264%   $40.5931   $40.59   $40.60   $40.60  
  Purchase #5 $246.36   4.380%   $257.1506   $257.15   $257.15   $257.20  
  Purchase #6 $175.96   4.834%   $184.4659   $184.47   $184.45   $184.50  
  Purchase #7 $167.26   5.148%   $175.8705   $175.87   $175.85   $175.90  
  7 purchase totals = $936.03       $994.2094   $994.21   $994.15   $994.40