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 $196.74   12.426%   $221.1869   $221.19   $221.20   $221.20  
  Purchase #2 $220.61   10.467%   $243.7012   $243.70   $243.70   $243.70  
  Purchase #3 $44.26   9.646%   $48.5293   $48.53   $48.55   $48.50  
  Purchase #4 $150.51   10.380%   $166.1329   $166.13   $166.15   $166.10  
  Purchase #5 $123.61   4.502%   $129.1749   $129.17   $129.15   $129.20  
  Purchase #6 $39.40   10.709%   $43.6193   $43.62   $43.60   $43.60  
  Purchase #7 $156.31   3.539%   $161.8418   $161.84   $161.85   $161.80  
  7 purchase totals = $931.44       $1,014.1863   $1,014.18   $1,014.20   $1,014.10