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 $177.69   13.117%   $200.9976   $201.00   $201.00   $201.00  
  Purchase #2 $207.31   8.854%   $225.6652   $225.67   $225.65   $225.70  
  Purchase #3 $228.67   13.492%   $259.5222   $259.52   $259.50   $259.50  
  Purchase #4 $191.71   12.611%   $215.8865   $215.89   $215.90   $215.90  
  Purchase #5 $43.68   3.490%   $45.2044   $45.20   $45.20   $45.20  
  Purchase #6 $75.32   6.817%   $80.4546   $80.45   $80.45   $80.50  
  Purchase #7 $83.46   8.454%   $90.5157   $90.52   $90.50   $90.50  
  7 purchase totals = $1,007.84       $1,118.2462   $1,118.25   $1,118.20   $1,118.30