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 $181.70   11.768%   $203.0825   $203.08   $203.10   $203.10  
  Purchase #2 $235.96   12.435%   $265.3016   $265.30   $265.30   $265.30  
  Purchase #3 $20.78   7.729%   $22.3861   $22.39   $22.40   $22.40  
  Purchase #4 $92.62   11.490%   $103.262   $103.26   $103.25   $103.30  
  Purchase #5 $165.52   9.652%   $181.496   $181.50   $181.50   $181.50  
  Purchase #6 $58.37   12.571%   $65.7077   $65.71   $65.70   $65.70  
  Purchase #7 $190.84   10.427%   $210.7389   $210.74   $210.75   $210.70  
  7 purchase totals = $945.79       $1,051.9748   $1,051.98   $1,052.00   $1,052.00