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 $126.60   11.623%   $141.3147   $141.31   $141.30   $141.30  
  Purchase #2 $226.74   3.694%   $235.1158   $235.12   $235.10   $235.10  
  Purchase #3 $44.36   11.685%   $49.5435   $49.54   $49.55   $49.50  
  Purchase #4 $188.77   7.686%   $203.2789   $203.28   $203.30   $203.30  
  Purchase #5 $241.73   11.490%   $269.5048   $269.50   $269.50   $269.50  
  Purchase #6 $76.53   9.801%   $84.0307   $84.03   $84.05   $84.00  
  Purchase #7 $75.33   6.598%   $80.3003   $80.30   $80.30   $80.30  
  7 purchase totals = $980.06       $1,063.0887   $1,063.08   $1,063.10   $1,063.00