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 $131.81   10.462%   $145.6   $145.60   $145.60   $145.60  
  Purchase #2 $246.38   12.363%   $276.84   $276.84   $276.85   $276.80  
  Purchase #3 $151.42   10.132%   $166.7619   $166.76   $166.75   $166.80  
  Purchase #4 $134.95   3.474%   $139.6382   $139.64   $139.65   $139.60  
  Purchase #5 $149.96   4.587%   $156.8387   $156.84   $156.85   $156.80  
  Purchase #6 $50.92   11.310%   $56.6791   $56.68   $56.70   $56.70  
  Purchase #7 $58.29   13.111%   $65.9324   $65.93   $65.95   $65.90  
  7 purchase totals = $923.73       $1,008.2903   $1,008.29   $1,008.35   $1,008.20