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 $143.31   13.645%   $162.8646   $162.86   $162.85   $162.90  
  Purchase #2 $103.45   5.435%   $109.0725   $109.07   $109.05   $109.10  
  Purchase #3 $155.45   9.516%   $170.2426   $170.24   $170.25   $170.20  
  Purchase #4 $12.89   6.474%   $13.7245   $13.72   $13.70   $13.70  
  Purchase #5 $86.87   4.841%   $91.0754   $91.08   $91.10   $91.10  
  Purchase #6 $189.72   6.180%   $201.4447   $201.44   $201.45   $201.40  
  Purchase #7 $231.28   5.465%   $243.9195   $243.92   $243.90   $243.90  
  7 purchase totals = $922.97       $992.3438   $992.33   $992.30   $992.30