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 $96.61   8.477%   $104.7996   $104.80   $104.80   $104.80  
  Purchase #2 $108.86   11.751%   $121.6521   $121.65   $121.65   $121.70  
  Purchase #3 $223.41   9.191%   $243.9436   $243.94   $243.95   $243.90  
  Purchase #4 $46.44   6.822%   $49.6081   $49.61   $49.60   $49.60  
  Purchase #5 $148.44   7.232%   $159.1752   $159.18   $159.20   $159.20  
  Purchase #6 $200.70   8.681%   $218.1228   $218.12   $218.10   $218.10  
  Purchase #7 $210.92   4.199%   $219.7765   $219.78   $219.80   $219.80  
  7 purchase totals = $1,035.38       $1,117.0779   $1,117.08   $1,117.10   $1,117.10