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 $222.84   11.102%   $247.5797   $247.58   $247.60   $247.60  
  Purchase #2 $193.59   3.851%   $201.0452   $201.05   $201.05   $201.00  
  Purchase #3 $150.85   4.128%   $157.0771   $157.08   $157.10   $157.10  
  Purchase #4 $22.67   3.739%   $23.5176   $23.52   $23.50   $23.50  
  Purchase #5 $201.55   5.665%   $212.9678   $212.97   $212.95   $213.00  
  Purchase #6 $104.78   4.781%   $109.7895   $109.79   $109.80   $109.80  
  Purchase #7 $248.80   7.394%   $267.1963   $267.20   $267.20   $267.20  
  7 purchase totals = $1,145.08       $1,219.1732   $1,219.19   $1,219.20   $1,219.20