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 $224.56   8.745%   $244.1978   $244.20   $244.20   $244.20  
  Purchase #2 $209.87   12.169%   $235.4091   $235.41   $235.40   $235.40  
  Purchase #3 $140.29   5.107%   $147.4546   $147.45   $147.45   $147.50  
  Purchase #4 $65.35   5.148%   $68.7142   $68.71   $68.70   $68.70  
  Purchase #5 $64.84   3.279%   $66.9661   $66.97   $66.95   $67.00  
  Purchase #6 $67.69   7.363%   $72.674   $72.67   $72.65   $72.70  
  Purchase #7 $201.44   9.794%   $221.169   $221.17   $221.15   $221.20  
  7 purchase totals = $974.04       $1,056.5848   $1,056.58   $1,056.50   $1,056.70