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 $68.30   8.474%   $74.0877   $74.09   $74.10   $74.10  
  Purchase #2 $171.57   5.606%   $181.1882   $181.19   $181.20   $181.20  
  Purchase #3 $56.76   13.720%   $64.5475   $64.55   $64.55   $64.50  
  Purchase #4 $198.31   4.217%   $206.6727   $206.67   $206.65   $206.70  
  Purchase #5 $181.65   12.178%   $203.7713   $203.77   $203.75   $203.80  
  Purchase #6 $131.89   7.539%   $141.8332   $141.83   $141.85   $141.80  
  Purchase #7 $62.96   12.743%   $70.983   $70.98   $71.00   $71.00  
  7 purchase totals = $871.44       $943.0836   $943.08   $943.10   $943.10