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 $173.48   12.197%   $194.6394   $194.64   $194.65   $194.60  
  Purchase #2 $90.96   7.460%   $97.7456   $97.75   $97.75   $97.70  
  Purchase #3 $38.44   7.623%   $41.3703   $41.37   $41.35   $41.40  
  Purchase #4 $58.41   7.639%   $62.8719   $62.87   $62.85   $62.90  
  Purchase #5 $209.64   6.735%   $223.7593   $223.76   $223.75   $223.80  
  Purchase #6 $170.52   3.788%   $176.9793   $176.98   $177.00   $177.00  
  Purchase #7 $200.65   6.483%   $213.6581   $213.66   $213.65   $213.70  
  7 purchase totals = $942.10       $1,011.0239   $1,011.03   $1,011.00   $1,011.10