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 $175.60   10.482%   $194.0064   $194.01   $194.00   $194.00  
  Purchase #2 $222.81   5.570%   $235.2205   $235.22   $235.20   $235.20  
  Purchase #3 $171.69   11.421%   $191.2987   $191.30   $191.30   $191.30  
  Purchase #4 $24.42   13.322%   $27.6732   $27.67   $27.65   $27.70  
  Purchase #5 $87.45   13.278%   $99.0616   $99.06   $99.05   $99.10  
  Purchase #6 $222.96   8.466%   $241.8358   $241.84   $241.85   $241.80  
  Purchase #7 $74.26   10.677%   $82.1887   $82.19   $82.20   $82.20  
  7 purchase totals = $979.19       $1,071.2849   $1,071.29   $1,071.25   $1,071.30