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 $60.84   13.288%   $68.9244   $68.92   $68.90   $68.90  
  Purchase #2 $81.87   8.276%   $88.6456   $88.65   $88.65   $88.60  
  Purchase #3 $191.33   5.721%   $202.276   $202.28   $202.30   $202.30  
  Purchase #4 $206.39   5.869%   $218.503   $218.50   $218.50   $218.50  
  Purchase #5 $195.77   11.710%   $218.6947   $218.69   $218.70   $218.70  
  Purchase #6 $63.42   5.363%   $66.8212   $66.82   $66.80   $66.80  
  Purchase #7 $160.59   4.568%   $167.9258   $167.93   $167.95   $167.90  
  7 purchase totals = $960.21       $1,031.7907   $1,031.79   $1,031.80   $1,031.70