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 $236.83   11.351%   $263.7126   $263.71   $263.70   $263.70  
  Purchase #2 $85.84   10.155%   $94.5571   $94.56   $94.55   $94.60  
  Purchase #3 $77.39   3.214%   $79.8773   $79.88   $79.90   $79.90  
  Purchase #4 $202.51   8.363%   $219.4459   $219.45   $219.45   $219.40  
  Purchase #5 $152.62   8.650%   $165.8216   $165.82   $165.80   $165.80  
  Purchase #6 $24.82   10.548%   $27.438   $27.44   $27.45   $27.40  
  Purchase #7 $161.30   12.457%   $181.3931   $181.39   $181.40   $181.40  
  7 purchase totals = $941.31       $1,032.2456   $1,032.25   $1,032.25   $1,032.20