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 $231.43   12.704%   $260.8309   $260.83   $260.85   $260.80  
  Purchase #2 $169.27   8.826%   $184.2098   $184.21   $184.20   $184.20  
  Purchase #3 $63.64   11.519%   $70.9707   $70.97   $70.95   $71.00  
  Purchase #4 $180.41   11.617%   $201.3682   $201.37   $201.35   $201.40  
  Purchase #5 $163.31   6.785%   $174.3906   $174.39   $174.40   $174.40  
  Purchase #6 $57.67   4.814%   $60.4462   $60.45   $60.45   $60.40  
  Purchase #7 $160.82   12.732%   $181.2956   $181.30   $181.30   $181.30  
  7 purchase totals = $1,026.55       $1,133.5120   $1,133.52   $1,133.50   $1,133.50