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 $171.33   12.124%   $192.102   $192.10   $192.10   $192.10  
  Purchase #2 $56.96   7.424%   $61.1887   $61.19   $61.20   $61.20  
  Purchase #3 $185.39   6.717%   $197.8426   $197.84   $197.85   $197.80  
  Purchase #4 $85.82   3.141%   $88.5156   $88.52   $88.50   $88.50  
  Purchase #5 $194.64   5.400%   $205.1506   $205.15   $205.15   $205.20  
  Purchase #6 $235.34   11.383%   $262.1288   $262.13   $262.15   $262.10  
  Purchase #7 $55.76   12.407%   $62.6781   $62.68   $62.70   $62.70  
  7 purchase totals = $985.24       $1,069.6064   $1,069.61   $1,069.65   $1,069.60